How to Clean Flux Residue After Soldering?

Once the soldering process is done some flux residue is seen on the surface. These fluxes are reactive chemicals, which if left unattended on the board surface, can lead to corrosion and eventually to circuit failures.

If your boards contain some high-impedance analogue circuits, then this flux poses a real concern due to conductivity issues. Leakage current through this flux is often in the root of an error in these circuits. If you are dealing with other types of circuits, then this residual flux poses a reliability issue. Thus, it is often required to remove this flux residue from the board. Removal of this residue also makes the boards look cleaner and tidier. Now the question that arises is how to clean this flux residue.

People have tried various ways to clean this residue.

Using a paint brush cleaner works for cleaning flux residue too. You can submerge the assembled board in a container that is filled with this and agitate it for some 30 sec. Then rinse it with water and pat it dry. To ensure that the board is completely moisture-free, give it a few passes of the heat gun.

You can also use the solder flux cleaner that is available in the market, but care should be taken while buying the one. Some fluxes get corrosive over time and hence they can intrude into the parts thereby creating some undesired effects. Even if you buy a good flux, it can become corrosive if contaminated. So, care should be taken while handling the product.

You can find solder flux remover that can absorb moisture from the air. If you use such stuff in high impedance circuit board, then you are in for a long-term problem.

It is advised to use rosin-based flux as it’s not conductive at low temperatures. It gets black or caramel colour only when it is exposed to very high temperatures.

No-clean flux, as the name suggests, is no-clean. You can leave it on the board without any problem.

Isopropyl alcohol is used as flux remover in electronics as it does not attack the plastic parts. It is known to be perfectly safe for use in electronics.

If you are using any water-soluble flux, it needs to be removed immediately as it is hygroscopic and thus a soap-scum like residue is left on the board making the entire thing conductive.

To be honest, every kind of flux has its own specific flux remover. These removers can be very limited or broad spectrum. To remove any kind of flux, you need to apply a lot of removers. Squirting some tiny bits never work. After applying the remover, leave it for few seconds and then brush it away. Always apply warm air to dry, but it should never be blown using your mouth. This is because human breath contains saliva, which is acidic in nature and hence can cause a problem.